It is generally known that a wheel bearing apparatus can support a vehicle wheel relative to a suspension apparatus. Also, a wheel speed detecting apparatus to detect a rotation speed of the vehicle wheel and to control the anti-lock braking system (ABS) is incorporated with the wheel bearing apparatus. Such a bearing apparatus generally includes a wheel speed detecting apparatus with a magnetic encoder having magnetic poles alternately arranged along its circumferential direction. The encoder is integrated in a sealing apparatus arranged between inner and outer members to contain rolling elements (balls or rollers). Further, a wheel speed detecting sensor is included to detect the variation in the magnetic poles of the magnetic encoder according to the rotation of the wheel.
The wheel speed sensor is usually mounted on a knuckle after the wheel bearing apparatus is mounted on the knuckle to form a suspension apparatus. Recently, a wheel bearing apparatus incorporating a wheel speed detecting apparatus has been proposed. Generally, the wheel speed detecting sensor is self-contained within the wheel bearing in order to reduce the size of the wheel bearing apparatus as well as to eliminate a troublesome air gap adjustment between the wheel speed sensor and the magnetic encoder.
An example of a wheel bearing apparatus incorporating a wheel speed detecting apparatus is shown in Japanese Laid-open Patent Publication No. 2003-254985, as shown in FIG. 7. This wheel bearing apparatus with an incorporated wheel speed detecting apparatus has an outer member 51 which forms a stationary member secured on a suspension apparatus (not shown). A wheel hub 55 and an inner member 52, which includes the wheel hub 55 and an inner ring 56, are inserted in the outer member 51 via a double row rolling elements (balls) 53 and 53. The outer member 51 has an integral wheel mount flange 51b at one end and double row outer raceway surfaces 51a and 51a formed on its inner circumferential surface. The inner member 52 is formed with double row inner raceway surfaces 55a and 56a opposite to the double row outer raceway surfaces 51a and 51a. One (55a) of the double row inner raceway surfaces is formed on the outer circumferential surface of the wheel hub 55 and the other (56a) is formed on the outer circumferential surface of the inner ring 56. The inner ring 56 is press-fit on the cylindrical portion 55b which extends axially from the inner raceway surface 55a of the wheel hub 55. The double row rolling elements 53 and 53 are arranged between the outer and inner raceway surfaces (51a, 51a) and (55a, 56a), respectively, and rotatably held by cages 57 and 57.
The wheel hub 55 has an integrally formed wheel mount flange 54 to mount a wheel (not shown). Hub bolts 54a, to secure the wheel, are rigidly secured on the wheel mount flange 54 equidistant about its periphery. A serration 55c is formed on the inner circumferential surface of the wheel hub 55. A stem portion 61 of an outer joint member 60 is inserted into the serration 55c and forms the constant velocity universal joint (not shown). Seals 58 and 59 are arranged at both ends of the outer member 51 to prevent leakage of grease contained within the bearing as well as the ingress of rain water or dust.
The seal 59 of the inboard side, as shown in an enlarged view of FIG. 8, is fitted in the inner circumference at the end of the outer member 51. The seal 59 has a first sealing plate 62, and a second sealing plate 63 with an “L”-shaped cross-section. The second sealing plate 63 has a cylindrical portion 63a fitted on the outer circumference of the inner ring 56. A standing portion 63b extends radially outward from the cylindrical portion 63a. A magnetic encoder 64 is adhered, via vulcanized adhesion, on the outer surface of the standing portion 63b. The magnetic encoder 64 is formed of rubberized magnet. The magnetic poles N and S are alternately arranged along the circumferential direction.
The first sealing plate 62 includes a metal core 65 with a substantially “L”-shaped cross-section. A sealing member 66, including a side lip 66a, is in sliding contact with the inner side surface of the standing portion 63b of the second sealing plate 63. A pair of radial lips 66b and 66c are in sliding contact with the cylindrical portion 63a of the second sealing plate 63.
An annular sensor holder 69 is mounted on one end of the outer member 51. The annular sensor holder 69 has a fitting cylinder 67 and a holding portion 68 connected to the fitting cylinder 67. The fitting cylinder 67 has an annular configuration with an “L”-shaped cross-section defined by a cylindrical portion 67a and a flange portion 67b which extends radially inward from the cylindrical portion 67a. 
The holding portion 68 is made by molding synthetic resin to an annular body where a wheel speed sensor 70 is embedded in the resin. The wheel speed sensor 70 is arranged opposite to the magnetic encoder 64, via a predetermined air gap therebetween. The wheel speed sensor 70 includes a magnetic detecting element such as a Hall element, a magnetic resistance element (MR element) etc. which changes characteristics in accordance with the flowing direction of magnetic flux. An IC is incorporated with a waveform shaping circuit to shape the output waveform of the magnetic detecting element.
A labyrinth seal is formed by a small gap 71 arranged between the flange portion 67b of the fitting cylinder 67 and the end surface of the inner ring 56. This prevent ingress of foreign matter, such as magnetic powder, into a space between the magnetic encoder 64 and the detecting portion of the wheel speed sensor 70 from outside of the bearing apparatus. However, this occurs before the stem portion 61 of the outer joint member 60 is inserted into the wheel hub 55 which includes a course in which the bearing apparatus is transferred to an assemble line of a manufacturer of an automobile. Accordingly, the reliability of detecting the rotation speed of the wheel can be improved.
However, although the wheel bearing apparatus with the incorporated wheel speed detecting apparatus of the prior art has a superior effect mentioned above, it is impossible to prevent ingress of foreign matter, such as magnetic powder, into a space between the magnetic encoder 64 and the detecting portion of the wheel speed sensor 70 from the outside of the bearing apparatus under severe circumstances during real running of the vehicle.